Where Does Stormwater Go?

Cities, those dense congregations of people  and buildings, have made possible economies   and lifestyles our early ancestors could  never have imagined. Whether you thrive in   or despise the concrete jungle, there’s no  denying its benefits. Putting all the people,   houses, jobs, stores, offices, and diversions  in one place gives us humans opportunities   that wouldn’t be possible if we all lived agrarian  lifestyles spread out across the countryside. But,   there are some negative consequences that come  from cramming so much into such a small area.   At no time is this more clear than when it rains.  Managing the flow of runoff through a city is an   immensely complex challenge that affects us in so  many ways from public safety to property rights,   from the environment to the health and  welfare of citizens. Hey, I’m Grady, and   this is Practical Engineering. On today’s episode,  we’re talking about urban stormwater management. This video is sponsored by  Curiosity Stream and Nebula.   Get 26% off at the link in the  description. More on that later! The water cycle is one of the most basic science  lessons we learn. So basic, in fact, that it’s   easy to forget how relevant and important it is  to our lives. Take a look out your window when   it’s raining, even when it’s raining hard, and  it doesn’t seem that significant. Some of the   rain soaks into the ground, some gets taken  up by plants, some gets caught in puddles,   and some runs off downhill, usually into the  street. One of the biggest challenges in a   city is the proportions of all these different  paths the water can take. All those streets,   sidewalks, buildings, and parking lots cover the  ground with impervious surfaces, which means that   instead of water infiltrating, it runs off toward  creeks and rivers, swelling them faster and higher   and filling them with more pollution. One  of the biggest impacts on the environment   of building anything is its effect on how water  moves above and below the ground during storms.   Multiply that to the scale of a city and you  can see how remarkably we modify our landscape.   Instead of acting like a sponge to absorb  rainwater as it falls, urban watersheds act   like funnels, gathering and concentrating  rainwater runoff. In this video, I want to   walk you through some of the infrastructure  cities use to manage this massive challenge   and a few new ideas in stormwater management  that are slowly taking hold in urban areas. Like most of the biggest challenges of  building and maintaining a civilization,   the negative impacts from adding impervious cover  don’t befall the property owner doing the adding,   but rather the people downstream. Just  like dumping pollution into the river   carries away to the next guy, it’s  easy to make bad drainage decisions   into someone else’s problem. That’s why most large  cities have rules about how to manage runoff and   flooding when new buildings or neighborhoods  get built. Drainage reviews are just a normal   part of the process of obtaining a building  permit these days. If you live in a major city,   just do a search for your local drainage manual  to see the kinds of things that are required.   Increased runoff has been a problem since people  started living in cities in the first place, and   the first way we handled it was simply to get the  water out and away as quickly as possible. That’s   because runoff creates flooding, and flooding  causes billions of dollars of property damage   and many lives each year. This solution is in the  name we still use for how cities manage storms:   “drainage.” When it rains or when it pours,  we try to give that runoff somewhere to go. Most cities are organized so the streets serve as  the first path of flow for rainfall. Individual   lots are graded with a slope toward the street  so that water flows away from buildings where it   would otherwise cause problems. The standard city  street has a crown in the center with gutters on   either side for water to flow. This keeps the  road mainly dry and safe for vehicle travel   while providing a channel to convey runoff.  But the streets aren’t the end of the line.   Eventually, the road will reach a  natural low point and start back uphill   or will have collected so much runoff  that it can’t hold it all in the gutter. At this point, the water needs a dedicated  system to carry it away. In the past,   it was common to simply put all the runoff from  the streets directly into the sewage system.   It’s a well-developed network of pipes flowing  by gravity out of the City… why not use it for   stormwater too? Well, actually there’s a really  good reason not to do that. At the end of each   sanitary sewer system is a wastewater treatment  plant that was almost certainly not designed to   process a massive influx of combined sewage and  stormwater runoff at the whims of mother nature.   In the worst cases, these plants have to release  untreated wastewater directly into waterways when   it is too much to be stored or processed. That’s  why most cities now use municipal separate storm   sewer systems, usually abbreviated as MS4s. These  are networks of ditches, curbs, gutters, sewer   pipes, and outfalls solely dedicated to moving  runoff from everywhere in the city to the natural   waterways that eventually carry it away. These  inlets aren’t just places for clowns to hang out,   they usually represent a direct path between  the street and the nearest creek or river.   Just to be clear, there’s not usually any  type of treatment happening along the way.   These sewers are not for waste. Whatever  you put into the storm sewer system   goes directly into a waterway, so  please don’t dump stuff in there. It’s easy to see why cities try so hard to get  stormwater out as fast as possible if you look   at the floodplain. This is just the area most  likely to be inundated during a major flood.   Land is one of the most valuable things  within a city, but its value goes way down   if it is exposed to flood risk. No one wants to  build something on land that could be flooded.   That being said, humans are notoriously bad at  assessing risk, and no matter where you look,   you’re likely to find development near creeks and  rivers. Getting the water out quickly reduces the   depth of flooding and thus shrinks the floodplain.  That’s a big reason why you see natural waterways   in cities enlarged, straightened, and lined  with concrete. You can see in my demo,   for the same amount of flow, the channel with  lots of vegetation moves water more slowly   and thus at a higher depth. The channel with  smooth sides gets the water moving faster,   and thus reduces the depth of flooding. But,  channelization isn’t all it’s cut out to be. It’s   ugly for one. No one wants a big, dirty concrete  channel as a part of their surroundings. But,   channelization also worsens flooding downstream  for the next guy and degrades the habitat of   the original waterway. It didn’t take long for  cities to realize you can’t just keep widening   and lining channels to keep up with the  increased runoff from more and more development. That’s why most cities now require developers  to take responsibility for their own   increase in runoff. By and large, that  means on-site storage for stormwater.   Retention and detention ponds act like  mini-sponges, absorbing all the rain   that rushes off the buildings, streets, and  parking lots and releasing it slowly back   into waterways. This shaves off the peak  of the runoff with the goal of reducing it   back down to or less than it was before all  those buildings and parking lots got built.   They also help reduce pollution by slowing down  the water so suspended particles can settle out. Onsite storage is a pretty effective  solution, and one you’ll see   everywhere if you’re paying attention. But it  still treats stormwater as a waste product,   something to be gotten rid of. The reality is  that rain is a resource, and natural watersheds   do a lot more than just getting rid of  it. They serve as habitat for wildlife,   they naturally clean runoff with vegetation, they  divert rain into the ground to recharge aquifers,   and they reduce flooding by slowing down the water  at the source rather than letting it quickly wash   away and concentrate. That’s why many cities  are moving toward ways to replicate and recreate   natural watershed functions within developed  areas. In the U.S., this is called low-impact   development and it includes strategies like  rain gardens, vegetated rooftops, rain barrels,   and other ways to bring more harmony between the  built environment and its original hydrologic and   ecological functions. It can also include better  management of the floodplain by using it for   purposes less vulnerable to flooding like parks  and trails. One low-impact strategy is permeable   pavement, and I have a video just on that topic  if you want to check it out after this one. One thing I have to mention when talking about  flooding is vehicle crossings. Any location where   a waterway and a road cross paths, whether it’s  a bridge, a culvert, or a low water crossing,   there’s always a chance of flooding  getting so bad that it overtops the road.   If you ever see water over the top of a roadway,  just turn around. Half of all flood-related deaths   happen when someone tries to drive a car or  truck through water over a road. If you can’t   see the road you have no idea how deep the water  is, and even if you can, it only takes a small   amount of swift water to push a vehicle down into  a river or creek. Water is heavy. Even when it’s   flowing slowly, floodwaters can impart a massive  force on a vehicle. Even if it didn’t, most cars   will float once the water reaches the floorboard  anyway. Some cities have warning systems to help   block roads when they’re overtopped by floods,  but it’s not something you should count on.   It just isn’t worth the risk. Find another  way. As they say: Turn around, don’t drown. Just like cities represent a colossal alteration  of the landscape and thus the natural water cycle,   we’re also going through a colossal shift in how  we think about rainfall and stormwater and how we   value the processes of natural watersheds. Look  carefully as you travel through your city and   you’ll notice all the different pieces and parts  of infrastructure that help manage water during   storm events. You’ll see plenty of ways to get  water out and away from buildings and streets,   but you hopefully also notice elements  of Low Impact Design - ways of harnessing   and benefitting from stormwater on-site,  treating it like the resource it truly is. If you’re here at the end of this video, I have  to assume that you spend your valuable free time   learning new things about the world.  You also probably don’t have time to   listen to a bunch of ads, which is perfect  because Nebula doesn’t have any. Nebula is a   streaming service built by and for independent  creators like MinutePhysics, Real Engineering,   Wendover Productions, and a bunch of others. It’s  a way for us to try new ideas and longer videos   that might not work on YouTube. And, we’re super  excited to be partnering with CuriosityStream,   a service with thousands of documentaries and  non-fiction titles on pretty much every subject   you can imagine. CuriosityStream loves independent  creators and wants to help us grow our platform,   so they’re offering free access to Nebula  when you sign up at CuriosityStream.com/   practicalengineering. There are a  lot of streaming services right now,   and if you add them all up it would be hundreds of  dollars a month. That’s why this bundle is such an   awesome deal. For a short time, CuriosityStream is  taking 26% off an annual plan - that’s $15 a year   to get access to thousands of awesome  documentaries on CuriosityStream   AND everything on Nebula as well. Watch how the  Hubble telescope’s images get created or a deep   dive into swiss watchmaking on CuriosityStream or  watch Tom Scott pit other YouTubers against each   other in his Nebula-exclusive gameshow, Money.  It’s a great way to support my channel and a whole   host of your other favorite educational creators.  Plus it’s just a good deal. Do us both a favor and   click that link in the description. Thank you  for watching, and let me know what you think!

Channel: Practical Engineering

Views: 796,695

Rating: 4.9423976 out of 5

Keywords: stormwater, urban stormwater, flooding, watershed, rain, rainwater, runoff, pollution, drainage, sewerwater, sewer system, gutter, flood risk, vegetation, concrete, channel, retention, detention, pond, waterway, onsite storage, aquifer, low impact design, LIT, permeable, pavement, impervious, rain garden, green roof, steel grating, reservoir, Practical Engineering, Civil Engineering, Engineer, Grady

Id: wdcXmerZWDc

Length: 11min 47sec (707 seconds)

Published: Tue Nov 03 2020

Reddit Comments

[u/Iron_Turtle_Dicks]

In Houston, it's managed very poorly.

[u/1wiseguy]

Phoenix is a bit different. Rain water pretty much all goes into local basins, where it stays until it seeps into the ground. It doesn't flow downhill into the ocean.

[u/OliverHPerry]

Love this channel.

[u/kaihatsusha]

Tokyo's storm vault system is pretty famous:

https://www.youtube.com/watch?v=Rp2l6nFIsZA

[u/Riverb0atGambler]

In Georgia they have been adopting the use of detention ponds and on most all roadway projects. The video didn't mention this but detention ponds can also help keep some oils out of streams by designing the outlet of the pond to only drain from below the surface of the water.

[u/johnnysolids]

Gotta love the practical engineer. This video got le talking to some guys in urban planning and this is one of those thing technical people find fascinating but the “public” doesn’t care until the floods or the sinkholes start coming in. Is their a way to actually start working on this without upsetting the NIBY crowd?

[u/JetDagger01]

With great difficulty is the short answer,

Source - am a urban stormwater engineer aswell

[u/kikenazz]

They don't

[u/LevoiHook]

I believe after the new Orleans disaster, some Dutch water management experts where sent in to explain how the Dutch manage ( being a very flat country with subsidence problems). Basically the conclusion was, they allocate more recourses. The problem is not so much a technical one as a democratic priorities one.